Lactobacillus casei의 고농도 배양에서 젖산 생산 및 부산물 생성

학위논문(박사) - 한국과학기술원 : 화학공학과, 1997.2, [ xi, 107 p. ]With the aim to produce lactic acid at a reduced medium cost, various complex nitrogen sources were examined in batch cultures of Lactobacillus casei subsp. rhamnosus. Among the sources tested, yeast extract (YE) enhanced lactic acid production most significantly. The addition of B vitamins of less than 25 mg/L enhanced lactic acid production to some extent in all cases except the media supplemented with nitrogen sources of casein origin. Batch fermentations were performed in order to find an optimum pH for both lactic acid production and by-products minimization. While a pH range of 6.0 - 6.5 was optimal for cell growth and lactic acid production, superior results were achieved at pH 6.0 when both maximum lactic acid productivity and minimum by-product formation were considered. Among the techniques that can increase cell concentration in the bioreactor, cell recycle using a hollow fiber filter and cell immobilization were studied. A continuous fermentor with a partial cell recycle was employed in order to investigate the physiological effects of cultivating L. casei at a high cell density in terms of by-products formation such as acetic acid, formic acid, ethanol, and \% D-lactic acid. The increase of by-products formation in the recycle fermentor was more significantly connected with substrate limitation resulted from a lower dilution rate rather than the cell concentration. The immobilization method of cells was developed using alginate capsules that possess an interphasic membrane and a liquid-core. The capsules were found to offer more space for cellular growth than gel-core beads, and allowed 1.5-fold higher cell concentration than the latter. However, the Ca-alginate structure was unstable during repeated batch fermentations for lactic acid production. Stable lactic acid production was possible in batch culture by cells immobilized in chitosan-coated Ba-alginate capsules. The cell leakage from the capsules was maintained relatively low during repeated b...한국과학기술원 : 화학공학과

Effect of nitrogen source on lactic acid fermentation and high cell density culture

학위논문(석사) - 한국과학기술원 : 화학공학과, 1993.2, [ viii, 60 p. ]한국과학기술원 : 화학공학과

A Novel Strategy for the Microbial Removal of Heavy Metals: Cell-surface Display of Peptides

Cell surface engineering is a rapidly developing technology of microorganism that achieves modification of cell surface function by joining external functional peptides with surface anchoring proteins, for example, Outer Member Protein (OMP). On account of these proteins possessing metal responsive motifs, they can be specifically used for metal adsorption and dissociation. To elucidate the problems caused by heavy metals and develop various technologies for their removel or recovery, various metalbinding proteins/peptides fused on microorganism cell surface have been applied as novel methods. During the past few years, bacterial cell surface display strategy has received growing attention for their availability to eliminate heavy metals. In this paper, the existing problems, progress, and suggestions for furture of the peptide displaying system are summarized